U.S. patent application number 09/732995 was filed with the patent office on 2002-07-25 for engine warm-up model and thermostat rationality diagnostic.
Invention is credited to Dawson, Gary D., Pallach, Gary M., Reese, Ronald A. II.
Application Number | 20020099482 09/732995 |
Document ID | / |
Family ID | 24945769 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020099482 |
Kind Code |
A1 |
Reese, Ronald A. II ; et
al. |
July 25, 2002 |
Engine warm-up model and thermostat rationality diagnostic
Abstract
A method is provided for diagnosing the rationality of a
thermostat in a motor vehicle. The method includes an engine
warm-up model and a thermostat diagnostic. The engine warm-up model
predicts the temperature that the engine coolant temperature should
be equal to at a given time after start-up. This is based on the
engine coolant temperature at start-up, ambient air temperature,
and how the vehicle is driven subsequent to start-up. This
predicted engine coolant temperature is compared to the actual
engine coolant temperature as read by an engine coolant temperature
sensor. The error between the predicted engine coolant temperature
and the actual engine coolant temperature is calculated and
integrated over time. The thermostat diagnostic runs at a
pre-selected time after start-up and compares the integrated error
to a calibrated threshold value. Depending upon the results of the
comparison, a pass, fail, or inconclusive condition is
determined.
Inventors: |
Reese, Ronald A. II;
(Goodrich, MI) ; Pallach, Gary M.; (Chesterfield,
MI) ; Dawson, Gary D.; (Rochester, MI) |
Correspondence
Address: |
Harness, Dickey & Pierce, P.L.C.
P.O. Box 828
Bloomfield Hills
MI
48303
US
|
Family ID: |
24945769 |
Appl. No.: |
09/732995 |
Filed: |
December 8, 2000 |
Current U.S.
Class: |
701/31.4 ;
123/540 |
Current CPC
Class: |
F01P 2023/00 20130101;
F01P 2037/02 20130101; F01P 2023/08 20130101; F01P 11/16 20130101;
F01P 11/14 20130101; F01P 2025/08 20130101; F01P 2031/00 20130101;
F01P 2025/13 20130101 |
Class at
Publication: |
701/29 ;
123/540 |
International
Class: |
G01M 017/00; F02M
015/00 |
Claims
What is claimed is:
1. A method of determining the functionality of a thermostat in a
motor vehicle comprising: determining a predicted engine coolant
temperature for the motor vehicle at a pre-selected time after
start-up; obtaining an actual engine coolant temperature for the
motor vehicle at the pre-selected time after start-up; comparing
said predicted engine coolant temperature to said actual engine
coolant temperature; deeming said thermostat to be functioning
properly if said actual engine coolant temperature is greater than
or equal to said predicted engine coolant temperature; and deeming
said thermostat to be functioning improperly if said actual engine
coolant temperature is less than said predicted engine coolant
temperature.
2. The method of claim 1 wherein said pre-selected time is
sufficient to ensure the actual engine coolant temperature is
greater than a minimum temperature threshold value where the engine
coolant responds to heat input and less than a thermostat opening
threshold value.
3. The method of claim 2 further comprising deeming said thermostat
to be functioning properly if said actual engine coolant
temperature is less than a pre-selected temperature difference from
said thermostat opening threshold value before said pre-selected
time after start-up.
4. The method of claim 1 wherein step of determining said predicted
engine coolant temperature further comprises combining a heat gain
value accounting for engine heat rejection to the engine coolant
with a heat loss value accounting for heat loss to ambient air and
heat loss through a heater core of the motor vehicle.
5. The method of claim 4 wherein an amount of said engine heat
rejection is obtained during said step of determining said
predicted engine coolant temperature from a look-up table using
engine speed as an input.
6. The method of claim 5 wherein said look-up table for engine heat
rejection is generated based on data obtained from a test engine
running on an engine dynamometer.
7. The method of claim 6 wherein said heat gain value accounting
for heat rejection is modified during said step of determining said
predicted engine coolant temperature to account for differences
between actual fuel to air ratio, actual ambient air temperature,
and actual engine coolant temperature and dynamometer fuel to air
ratio, dynamometer ambient air temperature, and dynamometer engine
coolant temperature.
8. The method of claim 4 wherein a value of said heat loss through
said heater core is based on engine speed.
9. The method of claim 4 wherein a value of said heat loss to
ambient air is based on vehicle speed.
10. The method of claim 4 wherein the combination of said heat gain
value and said heat loss value is integrated with respect to time
to yield said predicted engine coolant temperature.
11. The method of claim 1 wherein said comparing step further
comprises determining a difference between said actual engine
coolant temperature and said predicted engine coolant temperature
and integrating said difference with respect to time to obtain an
integrated difference value.
12. The method of claim 11 wherein said integrated difference value
is compared to a pass tolerance value and a fail tolerance value
during said comparing step.
13. The method of claim 1 further comprising determining that the
actual engine coolant temperature is not greater than ambient air
temperature by more than a pre-selected soak threshold value to
ensure that an adequate cold soak of the vehicle has occurred prior
to step of comparing said predicted engine coolant temperature to
said actual engine coolant temperature.
14. The method of claim 1 further comprising determining that an
ambient air temperature is greater than a minimum ambient air
threshold temperature prior to said step of comparing said
predicted engine coolant temperature to said actual engine coolant
temperature.
15. The method of claim 1 further comprising determining that an
ambient air temperature is less than a maximum ambient air
threshold temperature prior to said step of comparing said
predicted engine coolant temperature to said actual engine coolant
temperature.
16. The method of claim 1 further comprising determining that the
average vehicle speed is greater than a minimum average vehicle
threshold speed prior to said step of comparing said predicted
engine coolant temperature to said actual engine coolant
temperature.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to on board
diagnostic systems for motor vehicles, and more particularly to a
method for determining whether a thermostat in a motor vehicle is
operating properly.
BACKGROUND OF THE INVENTION
[0002] An on board diagnostic system is an emissions diagnostic
system whose purpose is to monitor all systems and components in a
vehicle that can affect emissions and to inform the driver of that
vehicle when an emissions-related problem has occurred. An
emissions-related problem is detected when either a system or a
deterioration of a system (or component thereof) causes vehicle
emissions to exceed certain pre-selected thresholds. On board
diagnostics are currently employed in passenger cars, light-duty
trucks, and medium-duty vehicles in all 50 states and Canada and
are quickly becoming used worldwide.
[0003] Generally, on board diagnostics check current operating
conditions against enable conditions to determine if any monitoring
program should run. If enabled, the monitoring program performs
calculations based on certain sensor information and other related
variables. The resulting diagnostic parameters are then checked
against calibrated threshold values. These threshold values are
typically correlated to emissions performance through standardized
test procedures. If the resulting diagnostic parameters are less
than the calibrated threshold values, then a pass status is
processed. If the resulting diagnostic parameters are greater than
the thresholds, then a fail status is processed. The on board
diagnostics system typically processes a failure by illuminating
the "Check Engine" malfunction indicator lamp on the instrument
panel and stores a fault code in the powertrain controller for
later retrieval by a service technician.
[0004] Although many vehicle system components are monitored by way
of conventional on board diagnostic systems, there is no diagnostic
which monitors whether the thermostat of a motor vehicle is
operating properly. Accordingly, it would be desirable to provide
an on board diagnostic for determining whether a thermostat in a
motor vehicle is operating properly.
SUMMARY OF THE INVENTION
[0005] The above and other objects are provided by a method which
includes an engine warm-up model and a thermostat diagnostic. The
engine warm-up model predicts the temperature that the engine
coolant temperature should be equal to at a given time after
start-up. This is based on the engine coolant temperature at
start-up, ambient air temperature, and how the vehicle is driven
subsequent to start-up. This predicted engine coolant temperature
is compared to the actual engine coolant temperature as read by an
engine coolant temperature sensor. The error between the predicted
engine coolant temperature and the actual engine coolant
temperature is calculated and integrated over time. The thermostat
diagnostic runs at a pre-selected time after start-up and compares
the integrated error to a calibrated threshold value. Depending
upon the results of the comparison, a pass, fail, or inconclusive
condition is determined.
[0006] The calibrated threshold value is calculated to discern
between a properly operating thermostat operating in a vehicle
which is experiencing the maximum heat loss/minimum heat gain
possible and an improperly operating thermostat operating in a
vehicle which is experiencing the minimum heat loss/maximum heat
gain possible. The properly operating thermostat/maximum heat
loss/minimum heat gain scenario provides the slowest possible
engine coolant temperature warm-up for a vehicle. Conversely, the
improperly operating thermostat/minimum heat loss/maximum heat gain
scenario provides the fastest possible engine coolant temperature
warm-up for a vehicle.
[0007] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood however that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are intended for purposes of illustration only, since
various changes and modifications within the spirit and scope of
the invention will become apparent to those skilled in the art from
this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0009] FIG. 1 is a flowchart depicting an initialization feature of
the present invention;
[0010] FIG. 2 is a flowchart depicting an enable feature of the
present invention;
[0011] FIG. 3 is a flowchart depicting a warm-up model feature of
the present invention;
[0012] FIG. 4 is a flowchart depicting a first portion of a
thermostat diagnostic feature of the present invention;
[0013] FIG. 5 is a flowchart depicting a second portion of the
thermostat diagnostic feature of the present invention; and
[0014] FIG. 6 is a flowchart depicting a third portion of the
thermostat diagnostic feature of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The present invention is directed towards a method for
determining whether a thermostat in a motor vehicle is operating
properly. The method includes an engine warm-up model for
predicting what temperature the engine coolant temperature of the
motor vehicle should be at a given time of operation and a
thermostat diagnostic which determines whether the thermostat is
operating properly based on a comparison between the predicted
engine coolant temperature from the engine warm-up model and the
actual engine coolant temperature. The following description of the
invention will be supplemented with a description of the drawings
below.
[0016] First, the engine warm-up model will be described. The
engine warm-up model is based on a first-order thermal system. The
basic law employed is the conservation of energy:
q.sub.in-q.sub.out=q.sub.stored
[0017] The energy in term (q.sub.in) accounts for the amount of
heat rejected to the engine coolant by the engine due to the
combustion process and friction. The energy out term (q.sub.out)
includes factors that may cause the coolant to loose some of the
heat gained including convection from the engine to ambient air and
through the motor vehicle heater. The energy stored term
(q.sub.stored) treats the engine as a single lumped parameter
(i.e., solids and liquids) thereby accounting for the increase in
temperature of the coolant.
[0018] The energy in term, or heat gain, is based on a mapped heat
rejection surface produced during engine dynamometer heat rejection
tests. To acquire the heat gain term at any given time during
testing, normalized fuel mass flow rate and engine speed are used
as the input parameters to the heat rejection surface. The
normalized fuel mass flow rate and engine speed are accumulated
between executions of the test and averaged during each execution
to account for rapid changes that may occur, such as deceleration
fuel shut-off. A correction to the heat gain term is made to
account for differences between the actual fuel-to-air ratio,
charge air temperature (ACT) and the predicted coolant temperature
and the fuel-to-air ratio, charge air temperature and predicted
coolant temperature existing during the engine dynamometer heat
rejection tests.
[0019] The correction to the heat gain term is a ratio of
temperature differences. The difference is the derived "mean
combustion gas temperature" (T.sub.g) minus engine coolant
temperature. The mean combustion gas temperature is modeled as
function of the fuel-to-air ratio based on a curve developed by
Taylor in The Internal Combustion Engine in Theory and Practice,
the M.I.T. Press, 1986. The numerator of the ratio includes the
actual values for each parameter and accounts for differences in
the charge air temperature, while the denominator includes the
values from the dynamometer testing. The corrected energy in or
heat gain term is determined by the following equation: 1 q gain ,
corr = q gain , dyno * { { T g ( FA act ) + [ T chrgair , act - T
chrgair , dyno ] * C 1 } T c , pred T g ( FA dyno ) - T c , dyno
}
[0020] wherein
[0021] q.sub.gain,cor=the dynamometer heat rejection value
corrected for equivalence ratio, dynamometer engine coolant
temperature, dynamometer ambient air, and current charge air
temperature;
[0022] q.sub.gain,dyno=a selected value from a table of heat
rejection values obtained from the dynamometer heat rejection
testing;
[0023] FA.sub.act=the actual fuel-to-air ratio;
[0024] FA.sub.dyno=a selected value from a table of fuel-to-air
ratio values obtained from dynamometer heat rejection testing;
[0025] T.sub.g(FA.sub.xxx)=a selected value from a mean combustion
gas temperature lookup table for making corrections to heat gain as
a function of fuel-to-air ratio;
[0026] T.sub.chargeair,act=the actual charge air temperature;
[0027] T.sub.chargeair,dyno=the ambient air temperature at which
the dynamometer heat rejection data set was obtained;
[0028] C.sub.1=a multiplier of the difference between charge air
temperature and the ambient air temperature at which the
dynamometer heat rejection data set was obtained which yields the
combustion gas temperature offset;
[0029] T.sub.c,pred=the engine coolant temperature predicted by the
model; and
[0030] T.sub.c,dyno=the engine coolant temperature at which the
dynamometer heat rejection data set was obtained.
[0031] Testing has shown that there is a significant and consistent
time delay between the start of a vehicle and the initial response
of the engine coolant temperature sensor. This delay is attributed
to the time it takes to heat the solid block/head of the engine and
the liquid coolant/oil of the engine. This affect is accounted for
by delaying the transfer of heat to the coolant by one of two
methods: delay until the engine coolant temperature reaches a
calibrateable offset above the initial predicted engine coolant
temperature (which is set equal to the engine coolant temperature
after the start-to-run transition; or delay until a maximum
calibrated amount of time equal to the time it takes before the
coolant temperature responds to heat input after the fuel delivery
mode is set to start or run. The heat gain term used by subsequent
calculations is the delayed value which equals the dynamometer heat
rejection corrected for equivalence ratio, dynamometer engine
coolant temperature, dynamometer ambient air, and current charge
air temperature.
[0032] The energy out term, or heat loss, within the method is
modeled separately by the equation for Newton's Law of Cooling:
q.sub.loss=h*A*.DELTA.T
[0033] wherein
[0034] q.sub.loss=convention heat loss;
[0035] h=convection heat transfer coefficient;
[0036] A=nominal heat transfer surface area; and
[0037] .DELTA.T=temperature difference.
[0038] Heat loss from the coolant by convection to the ambient air
is dependent upon air velocity through the engine compartment.
Vehicle speed is used as a surrogate for air velocity. Vehicle
speed is normalized to 100 mph to make the value dimensionless,
raised to a power, and scaled to achieve the heat transfer
coefficient due to forced convection. Heat loss to the ambient air
due to natural convection is accounted for in the additive term of
the equation for the heat transfer coefficient as shown in the
equation below: 2 q loss , amb = { C 2 * [ V 100 mph ] n + C 3 } *
A amb * [ T c , pred - T amb ] = { C 2 * ( V norm ) n + C 3 } * A
amb * [ T c , pred - T htr , in ]
[0039] wherein
[0040] q.sub.loss,amb=the heat loss to ambient air based on vehicle
speed in miles per hour;
[0041] C.sub.2=the coefficient for ambient heat loss (heat transfer
coefficient), the value of a in the equation, h=A*(vehicle
speed/100).sup.n+B;
[0042] V=vehicle speed in miles per hour;
[0043] (V.sub.norm).sup.n=the value from an ambient air exponent
lookup table for heat transfer coefficients as a function of
vehicle speed, the value of (vehicle speed/100).sup.n in the
equation, h=A*(vehicle speed/100).sup.n+B;
[0044] A.sub.amb=the estimated area of engine surfaces which
contribute to convection heat losses to ambient air;
[0045] T.sub.c,pred=the engine coolant temperature predicted by the
model; and
[0046] T.sub.amb=ambient air temperature used for the system.
[0047] Heat loss from the coolant through the passenger compartment
heater is dependent on the coolant flow rate through the heater
core. Engine speed is used as a surrogate for coolant flow rate.
Engine speed is normalized to 1,000 rpm to make the value
dimensionless, raised to a power, and scaled to achieve the heat
transfer coefficient due to forced convection. In the model, air
flow across the heater core is assumed to be at its maximum value
(high blower/bi-level mode/full heat). The equation for calculating
the heat loss through the heater is shown below: 3 q loss , htr = {
C 4 * [ N 100 mph ] n } * A htr * [ T c , pred - T amb ] = { C4 * (
N norm ) n } * A htr * [ T c , pred - T amb ]
[0048] wherein
[0049] q.sub.loss,htr=the heat loss through the passenger
compartment heater based on engine speed;
[0050] C.sub.4=a coefficient for passenger compartment (heater
core) heat loss (heat transfer coefficient), the value of A in the
equation h=A*(engine speed/1,000).sup.n;
[0051] N=average vehicle engine speed;
[0052] (N.sub.norm).sup.n=a value from a heater exponent lookup
table for heat transfer coefficients as a function of engine speed,
the value of (engine speed/1,000).sup.n in the equation h=A*(engine
speed/1,000).sup.n;
[0053] A.sub.amb=the estimated area of the heater core (the heat
transfer surface) which contributes to convection heat losses to
the passenger compartment;
[0054] T.sub.c,pred=the engine coolant temperature predicted by the
model; and
[0055] T.sub.htr,in=the temperature of the air entering the
heater.
[0056] The energy balance equation is then solved to determine the
energy (or heat) stored in the lumped-mass engine system (engine
solid and engine fluids). This is done by subtracting the heat loss
term from the heat gain term. The value for the stored heat is
divided by the product of the mass (m) and specific heat (Cp) of
the engine and integrated with respect to time to obtain the
temperature change. The value of the integral is added to the
initial coolant temperature (i.e., when the engine is started) to
determine the predicted coolant temperature. Thus: 4 q stored = m *
Cp * T t q gain , corr , dly - q loss , amb * - q loss , htr = (
mCp ) corr * T t T c , pred = T c , act initial + q gain , corr dly
- q loss , amb - q loss , htr ( mCp ) corr t
[0057] wherein
[0058] T.sub.c,pred=the engine coolant temperature predicted by the
model;
[0059] T.sub.c,act,initial=the engine coolant temperature at the
initial start-to-run transition;
[0060] Q.sub.gain,corr,dlv=the dynamometer heat rejection value
corrected for equivalence ratio, dynamometer engine coolant
temperature, dynamometer ambient air, and current charge air
temperature after the delay time it takes before the coolant
temperature responds to heat input after startup;
[0061] Q.sub.loss,amb=the heat loss to ambient air based on vehicle
speed;
[0062] Q.sub.loss,htr=the heat loss through the passenger
compartment heater based on engine speed;
[0063] (mCp).sub.corr=the mass and specific heat product of the
engine mass corrected for the engine coolant temperature at
startup.
[0064] The product of the mass and specific heat is derived from
the system time constant which relates it to the ambient heat loss
term. This product is corrected as a function of the starting
coolant temperature to account for changes in specific heat.
Testing has shown that using the starting coolant temperature
yields more accurate results than the instantaneous temperature.
This is due in part to the fact that the system is modeled as a
single mass. The equation for the correction to the mass and
specific heat is indicated below:
(mCp).sub.corr=(mCp).sub.std*{C.sub.5*(T.sub.c,act.sub..sub.initial-T.sub.-
Cp,std)+1}
[0065] wherein
[0066] (mCp).sub.corr=the mass and specific heat product of the
engine corrected for startup engine coolant temperature;
[0067] (mCp).sub.std=a reference value of the mCp product at
standard conditions, the value of A in the equation,
mCp=A*(B*(startup engine coolant temperature-C)+1);
[0068] C.sub.5=a correction multiplier to account for changes in
the specific heat of the engine surfaces as a function of
temperature, the value of B in the equation, mCp=A*(B*(startup
engine coolant temperature-C)+1);
[0069] T.sub.c,act,initial=the engine coolant temperature at the
initial start-to-run transition; and
[0070] T.sub.Cp,std=the standard temperature of the specific heat
value, the value of C in the equation, mCp=A*(B*(startup engine
coolant temperature-C)+1).
[0071] Next, the thermostat diagnostic feature of the present
invention will be described. After the heat gain delay has been
achieved, the error between the predicted engine coolant
temperature and the actual engine coolant temperature is integrated
with respect to time. This integrated error is compared to error
thresholds to determine whether the thermostat is operating
properly or improperly.
[0072] Vehicles with properly operating thermostats yield
integrated errors greater than the pass threshold. Vehicles with
improperly operating thermostats yield integrated errors less than
the fail threshold. Separate pass and fail thresholds are
calibrated in order to improve the accuracy of the diagnostic
(i.e., minimize .alpha. and .beta. errors). This results in a
system tolerance range where otherwise valid trips that neither
pass nor fail are deemed inconclusive.
[0073] The thermostat diagnostic feature also determines at what
point during the trip the test should be performed. Extensive
testing and evaluation have found that performing the test at a
fixed predicted coolant temperature change from the starting
temperature provides reliable results. The maximum coolant
temperature at which the test occurs is limited to prevent the
interaction of an operating thermostat. The logic for selecting the
desired predicted coolant temperature at which to perform the test
is shown below: 5 ( T c , pred ) run = minimum { ( T c , pred ) max
T c , initial + ( T c , pred ) offset }
[0074] wherein
[0075] (T.sub.c,pred).sub.run=the threshold for the predicted
engine coolant temperature where the diagnostic test will run;
[0076] (T.sub.c,pred).sub.max=the maximum predicted engine coolant
temperature that the diagnostic will run;
[0077] (T.sub.c,pred).sub.offset=the offset temperature applied to
ambient air temperature to determine the predicted engine coolant
temperature at which the diagnostic will run; and
[0078] T.sub.c,initial=the engine coolant temperature at initial
start-to-run transition.
[0079] If the actual engine coolant temperature attains a
calibrated value before the predicted coolant temperature reaches
the test temperature, the test concludes that the vehicle has a
properly functioning thermostat. The calibrated value is set equal
to, for example, an engine coolant temperature pass threshold as
prescribed by an industry or government prescribed standard, i.e.,
within 20 degrees on the thermostat opening temperature.
[0080] The pass and fail thresholds are calibrated as a function of
ambient air temperature to account for the lower integrated errors
incurred when the coolant temperature increase during the trip is
limited by the maximum coolant temperature at which the test should
be performed. The pass threshold is defined in a calibrateable
value (the value of the lowest integrated error required to pass
the test). Similarly, the fail threshold is defined in a
calibrateable value (the value of the highest integrated error
required to fail the test). The difference between the actual
integrated error and the applicable threshold is reported as the
difference between the pass or fail threshold and the actual
integrated error.
[0081] Several factors may prevent the warm-up model from
accurately predicting the coolant temperature and therefor affect
the integrity of the thermostat rationality feature. The diagnostic
checks for these conditions and will neither pass nor fail a test
if one of the conditions exist. The existence of each condition
causes an internal bit to be set to designate the cause of the "no
test" circumstance. These conditions, for example, include a high
starting ambient temperature, a low starting ambient temperature,
an insufficient soak, a low average vehicle speed, and an
inconclusive error.
[0082] A trip conducted at a high ambient temperature (and therefor
high starting coolant temperature) does not allow the model to run
long enough to adequately accumulate error between the predicted
and actual coolant temperatures. The calibrateable to check against
for this condition is the maximum ambient temperature for the test
to run. This could be, for example, 100-110 degrees Fahrenheit. The
internal bit set if this condition exists is a flag to show the
diagnostic test was aborted due to the ambient temperature being
too high.
[0083] The accuracy of the warm-up model may be compromised at
extremely low temperatures. To account for this, a low temperature
disable is provided. The calibrateable to check against for this
condition is the minimum ambient temperature for the test to run.
This could be, for example, 20 to -10 degrees Fahrenheit. The
internal bit set if the condition exists is a flag to show the
diagnostic test was aborted due to the ambient temperature being
too low.
[0084] A large temperature difference between the starting coolant
temperature and the ambient air temperature may indicate that the
vehicle has not had an adequate cold soak and therefore may prevent
the warm-up model from providing an accurate prediction of the
engine coolant temperature. The calibrateable to check against for
this condition is the difference in temperature between the ambient
temperature and the engine coolant temperature at start-up. This
could be, for example, 5-15 degrees Fahrenheit. The internal bit
set if the condition exists is a flag to show the diagnostic test
was aborted due to an inadequate thermal soak of the vehicle.
[0085] Low vehicle speed conditions produce nearly the same engine
coolant temperature warm-up rates in vehicles with properly and
improperly functioning thermostats. The ability to correctly
diagnosis the condition of the thermostat is a function of the
ratio of the radiator heat loss to the heater heat loss. The heat
loss through the radiator must be greater than the maximum heat
loss possible through the heater. In order to maximize the
opportunity for a correct diagnosis, the vehicle must attain a
minimum average vehicle speed by the time the pass/fail
determination is made. The calibrateable to check against for this
condition is a minimum average vehicle speed threshold. This could
be, for example, 10-20 mph. The internal bit set if the condition
exists is a flag to show the diagnostic test was aborted due to the
average vehicle speed being too low.
[0086] Separate pass and fail thresholds must be calibrated in
order for an inconclusive error to be detected. The separate
thresholds provide a means to account for poor separation between
properly and improperly functioning thermostats, which may be
caused, for example, by operation of an air conditioning system.
The internal bit set if the condition exists is a flag to show that
the integrate error was lower than the pass threshold and higher
than the fail threshold. It should be noted that this condition is
different from an inconclusive test implied by a user dictated
condition in a task manager, which can occur when the bit
indicating that the thermostat rationality test is complete is set
while neither the thermostat rationality test pass bit nor
thermostat rationality test fail bit is set.
[0087] Additionally, in vehicles equipped with inlet-side
thermostats, it is possible to pull the thermostat open at high
engine speeds. The instantaneous engine speed is compared to a
calibrateable engine speed threshold during each execution of the
test. If the threshold is exceeded, a no fail aggressive timer is
incremented. During the rationality diagnostic, if the test
indicates that the integrated error is not above the pass
threshold, the timer value is compared to the calibrateable no fail
aggressive threshold value. If the threshold is exceeded, a no fail
aggressive flag is set and the trip neither passes or fails
(implied inconclusive).
[0088] Preferably, the diagnostic feature stores a fault code and
illuminates a malfunction indicator lamp after two failed trips
occur.
[0089] Turning now to the drawing figures, a description of the
present invention will be provided with reference to flow charts.
Referring to FIG. 1, the methodology starts its initialization at
10 and continues to 12 where the mass and specific heat product of
the engine mass including its solids and liquids, as corrected for
coolant temperature and ambient temperature at the initial
start-to-run transition, is calculated. From 12, the methodology
continues to 14 where it is determined whether the corrected mass
and specific heat product determined at 12 is greater than zero. If
not, the methodology advances to 16 and sets a flag indicating that
no test will run due to a non-compatible corrected mass and
specific heat product value. From 16 the methodology advances to 18
and ends pending a subsequent execution.
[0090] Referring again to 14, if the corrected mass and specific
heat product value is greater than zero, the methodology continues
to 20. In 20, the methodology sets the predicted engine coolant
temperature equal to the initial engine coolant temperature. At 22,
the methodology sets a temporary variable of predicted coolant
temperature according to the initial engine coolant temperature and
a scalar such as 16384. At 24, the methodology sets the predicted
engine coolant temperature threshold where the diagnostic feature
will run. Preferably, this threshold is set equal to the minimum of
(1) the maximum predicted engine coolant temperature that the
diagnostic will run and (2) the offset temperature applied to
ambient air temperature to determine the predicted engine coolant
temperature at which the diagnostic will run plus initial engine
coolant temperature.
[0091] In 26, the methodology determines whether the time since
startup is greater than a threshold value corresponding to the time
it takes before the coolant temperature will respond to heat input.
If so, at 28 the methodology stores the delay time period to use
before implementing the diagnostic feature equal to the threshold
value. If not, at 30 the methodology sets the delay time period to
use before implementing the diagnostic feature equal to the current
time period. From 28 and 30, the methodology advances through
connector A to 32 in FIG. 2.
[0092] Referring to FIG. 2, in 32 the methodology begins an
enablement sequence by determining if the fuel delivery mode of the
motor vehicle is in either a run mode or a start mode. If not, the
methodology waits for such a condition to exist prior to
proceeding. Once the condition is met at 32, the methodology
advances to 34.
[0093] In 34 the methodology determines whether any stop test flag
is set. For example, the methodology determines whether a limpin
flag is set indicating that the engine coolant volts are low; a
limpin flag is set indicating that the engine coolant volts are
high; a flag is set indicating that the thermostat rationality
needs to be disabled (for example due to a user set condition
(ambient temperature too high or low, vehicle speed too low, etc.)
which is desired to cause all on board diagnostics to stop); a flag
is set indicating that the thermostat rationality should be stopped
(for example due to a user set condition (ambient temperature too
high or low, vehicle speed too low, etc.) which is desired to cause
the thermostat rationality diagnostic to stop); a flag is set
indicating that a conflict condition (for example due to another on
board diagnostic running having greater priority); a flag is set
indicating that the calculation for the mass and specific heat
product was equal to or less than zero (block 16); a flag is set
indicating that the calculation for a predicted mean combustion gas
temperature corrected for ambient air temperature was equal to or
less than zero; or a flag is set indicating that the calculation
for a heat gain correction factor accounting for both engine
coolant temperature and ambient air temperature was equal to or
less than zero. If any stop test flag is set at 34, the methodology
does not run a test. In block 36 the methodology clears any
rationality diagnostic "in progress" flag and sets a test complete
flag. From 36 the methodology advances to 38 and ends pending a
subsequent execution.
[0094] Referring again to 34, if no stop test flag is set the
methodology advances through connector B to 40 in FIG. 3. Referring
to FIG. 3, in 40 the thermostat diagnostic begins and is preferably
run every 800 ms after the start-to-run transition. At 40 the
warm-up model begins by calculating the heat gain by retrieving the
equivalence ratio output from the dynamometer heat rejection
surface as a function of engine speed and the mass of fuel to be
delivered per cylinder this cycle. At 42 the methodology calculates
the predicted mean combustion gas temperature corrected for ambient
air temperature. Preferably this is accomplished by the following:
(filtered charge temperature)-(ambient air temperature at which the
dynamometer heat rejection data set was obtained)*(the multiplier
of the difference between the filtered charge temperature and
ambient air temperature at which the dynamometer heat rejection
data set was obtained to obtain the combustion gas temperature
offset)/16+the value of the mean combustion gas temperature from a
2d look-up table based on the open loop fuel-to-air ratio.
[0095] At 44 the methodology determines if the corrected mean
combustion gas temperature determined at 42 is less than or equal
to zero. If so, at 46 the methodology sets a flag indicating that
no test is being run due to an incompatible combustion gas
temperature value. From 46 the methodology advances to 48 and ends
pending a subsequent execution.
[0096] Referring again to 44, if the corrected mean combustion gas
temperature is greater than zero the methodology advances to 50. In
50 the methodology calculates the heat gain correction factor
according for both engine coolant temperature and ambient air
temperature. Preferably, this is based on the following: (the
predicted mean combustion gas temperature corrected for ambient air
temperature from 42-the engine coolant temperature predicted by the
model in 20)*128/(the value of the mean combustion gas temperature
from a 2d look-up table based on the equivalence ratio output from
dynamometer heat rejection surface as a function of engine speed
and the mass of fuel to be delivered per cylinder this cycle)-(the
engine coolant temperature at which the dynamometer heat rejection
data set was obtained).
[0097] In 52 the methodology determines if the heat gain correction
factor accounting for both engine coolant temperature and ambient
air temperature determined at 50 is less than or equal to zero. If
so no test is run and the methodology advances to 54. In 54 the
methodology sets a no test flag indicating that the ambient heat
gain factor was incompatible. From 54 the methodology advances to
48 and ends pending a subsequent execution.
[0098] Referring again to 52, if the corrected ambient heat gain
factor determined at 50 is greater than zero, the methodology
advances to 56. In 56 the methodology gets the dynamometer heat
rejection value corrected for equivalence ratio, dynamometer engine
coolant temperature, dynamometer ambient air, and current charge
air temperature. Preferably this is accomplished by the following:
(heat gain correction factor accounting for both engine coolant
temperature and ambient air temperature)*(the value of the heat
rejection obtained from dynamometer heat rejection testing from a
3d surface look-up table based on the mass of fuel to be delivered
per cylinder this cycle and at this engine speed)/128. This is the
energy in term.
[0099] In 58 the methodology begins to calculate heat loss by
calculating the engine box heat convection to ambient air. The heat
loss to ambient air is based on vehicle speed is preferably
determined according to the following: (the engine coolant
temperature predicted by the model at 20-the ambient temperature
used for the system)*((((estimated area of engine surfaces which
contribute to convection heat loss to ambient air*the value of a
heat transfer coefficient from a 2d ambient exponent lookup table
based on engine speed)/65536)*the heat transfer coefficient for
ambient heat loss/2.sup.8+the estimated area of engine surfaces
which contribute to convection heat losses to ambient air*the heat
transfer coefficient offset for ambient heat loss/65536))/512.
[0100] In 60 the methodology calculates the heat core heat loss.
The heat lost through the passenger compartment heater is based on
engine speed and is preferably determined as follows: (((the heat
transfer coefficient from a 2d table heater exponent lookup table
based on average engine speed*the estimated area of the heat
transfer surface of the heater core which contributes to convection
heat losses to the passenger compartment)/65536)*((the heat
transfer coefficient for passenger compartment heat loss*(the
engine coolant temperature predicted by the model at 20-the
temperature of the air entering the heater))/256))/128.
[0101] In 62 the methodology calculates the total heat lost to the
atmosphere and to the passenger compartment by adding the heat lost
to ambient air based on engine speed determined at 58 and the heat
lost through the passenger compartment heater based on engine speed
determined at 60. This is the energy out term.
[0102] In 64 the methodology begins temperature integration by
storing the dynamometer heat rejection corrected for equivalence
ratio, dynamometer engine coolant temperature, dynamometer ambient
air, and current charge air temperature as determined at 56 to a
buffer at a current time. This value is used in calculating the
total heat input to the coolant after the warm-up delay. In 66 the
methodology increments a heat gain warm-up delay counter.
[0103] In 68 the methodology determines whether the value of the
heat gain warm-up delay counter is greater than or equal to the
time it takes for the coolant temperature to respond to heat input
after startup as determined in 28 or 30 of FIG. 1 or if the engine
coolant temperature is greater than or equal to the predicted
engine coolant temperature plus a calibrated offset temperature. If
so, at 70 the methodology clears the heat gain warm-up delay
counter and at 72 sets a flag indicating that the required time
delay has been reached. From 72, or 68 if the heat gain warm-up
delay counter is less than the time it takes for the coolant
temperature to respond to heat input after startup, the methodology
continues to 74.
[0104] In 74 the methodology determines whether the flag indicating
that the time delay has been reached is set. If so, the methodology
continues to 76 and clears the value stored as the dynamometer heat
rejection value corrected for equivalence ratio, dynamometer engine
coolant temperature, dynamometer ambient air, and current charge
air temperature. If not, the methodology advances to 78 and sets
the dynamometer heat rejection value corrected for equivalence
ratio, dynamometer engine coolant temperature, dynamometer ambient
air, and current charge air temperature equal to the oldest
calculated heat gain stored in the buffer at 64 (which may be
scaled, such as by 4, if desired).
[0105] At 79 the methodology updates the vehicle speed and
determines the average vehicle speed. Further, if the engine speed
is greater than an engine speed threshold value, the methodology
increments the no fail aggressive timer.
[0106] At 80 the methodology sets the rate of predicted coolant
temperature change. Preferably, this is determined as follows: (the
dynamometer heat rejection value corrected for equivalence ratio,
dynamometer engine coolant temperature, dynamometer ambient air,
and current charge air temperature as determined at 76 or 78)-(the
total heat lost to the atmosphere and passenger compartment from
62)*16384/the mass and specific heat product corrected for startup
engine coolant temperature from 12.
[0107] At 82 the methodology determines the temporary variable of
predicted coolant temperature. This was initially set equal to the
startup engine coolant temperature at 22. Now the value is updated
according to the following: (the rate of predicted coolant
temperature change from 80)*0.8+(the previous temporary variable of
predicted coolant temperature from 22).
[0108] In 84 the methodology calculates the engine coolant
temperature predicted by the model. This is preferably accomplished
by setting it equal to: (the temporary variable of the predicted
coolant temperature determined at 82)/16384. From 84 the
methodology advances through connector C to 86 in FIG. 4.
[0109] Referring now to FIG. 4, in 86 the methodology begins the
thermostat diagnostic feature by calculating the accumulated
integrated error based on predicted engine coolant temperature and
actual engine coolant temperature. Preferably, the accumulated
integrated error is determined according to the following: (actual
engine coolant temperature*16384-the temporary variable of
predicted coolant temperature from 82)* 0.8+the previous
accumulated integrated error. In 88 the methodology calculates
integrated vehicle speed. This is preferably accomplished by the
following: vehicle speed in miles per hour*0.8+the previous
integrated vehicle speed.
[0110] In 90 the methodology calculates the average vehicle speed.
The average vehicle speed preferably determined by: the integrated
vehicle speed from 88/the time the engine has been running. In 92
the methodology sets a flag indicating that the thermostat
rationality test is in progress.
[0111] In 94 the methodology determines whether the temporary
variable of predicted coolant temperature from 82 is greater than
or equal to the threshold for the predicted engine coolant
temperature where the diagnostic test will run from 24. If so, the
methodology advances through connector D to 96 in FIG. 5. If not,
the methodology advances through connector E to 98 in FIG. 6.
[0112] Referring to FIG. 5, in 96 the methodology sets a plurality
of pre-selected values. For example, the methodology sets the
predicted engine coolant temperature at the time the diagnostic
test is run equal to the engine coolant temperature predicted by
the model at 84; the actual engine coolant temperature at the time
the diagnostic test is run equal to the actual engine coolant
temperature; the time since the start of the diagnostic test equal
to the engine run time since startup; the actual average speed at
the time the diagnostic test is run equal to the average vehicle
speed determined at 90; the integrated error value at the time the
diagnostic test is run equal to the accumulated integrated error
determined at 86; the actual ambient temperature at the time the
diagnostic test is run equal to the ambient temperature used for
the system; and sets a flag to show that the warm-up model based
thermostat rationality diagnostic has run.
[0113] In 100 the methodology determines whether a sufficient cold
engine soak has occurred. This is preferably accomplished by
determining if the engine coolant temperature at startup minus the
ambient air temperature is greater than a calibrateable threshold
such as 5 to 15 degrees Fahrenheit. If so, no test is run and the
methodology advances to 102. In 102 the methodology sets a flag to
show that the diagnostic test was aborted due to an inadequate
thermal soak of the vehicle, clears the flag indicating that the
rationality test was in progress, and sets a flag indicating that
the rationality test is complete. From 102, the methodology
advances to 104 and ends pending a subsequent execution.
[0114] Referring again to 100, if the startup engine coolant
temperature less the ambient air temperature is less than or equal
to the temperature threshold which ensures a sufficient soak, the
methodology continues to 106. In 106 the methodology determines if
the ambient air temperature is less than a minimum ambient air
temperature threshold for the test to run. This could be, for
example, 20 to -10 degrees Fahrenheit. If so, no test is run and
the methodology advances to 108. In 108 the methodology sets a flag
to show that the diagnostic test was aborted due to the ambient air
temperature being too low, clears the flag indicating that the
rationality test was in progress, and sets a flag indicating that
the rationality test is complete. From 108, the methodology
continues to 104 and ends pending a subsequent execution.
[0115] If the ambient air temperature is greater than or equal to
the minimum temperature at 106, the methodology continues to 110.
In 110 the methodology determines whether the ambient air
temperature is greater than the maximum ambient air temperature
threshold for the test to run. For example, this may be equal to
100 to 110 degrees Fahrenheit. If so, no test will run and the
methodology continues to 112. In 112 the methodology sets a flag to
show that the diagnostic test was aborted due to the ambient air
temperature being too high, clears a flag indicating that the test
is in progress and sets a test complete flag. From 112, the
methodology continues to 104 and ends pending a subsequent
execution.
[0116] If the ambient air temperature is less than or equal to the
maximum ambient temperature threshold at 110, the methodology
continues to 114. In 114 the methodology determines whether the
average vehicle speed is less than a minimum average vehicle speed
threshold. This may be, for example, 10 to 20 mph. If so, no test
is run and the methodology advances to 116. In 116 the methodology
sets a flag to show that the diagnostic test was aborted due to the
average vehicle speed being too low, clears a flag indicating that
the rationality test is in progress, and sets a test complete flag.
From 116, the methodology continues to 104 and ends pending a
subsequent execution.
[0117] If the average vehicle speed is greater than or equal to the
minimum average vehicle speed threshold at 114, the methodology
continues to 118. In 118 the methodology determines whether the
integrated error value at the time the diagnostic test was run is
greater than or equal to the value of the lowest integrated error
required to pass the test. This pass threshold value is acquired
from a 2d table lookup based on ambient air temperature. If so, the
methodology deems the thermostat to have passed the test and
advances to 120. In 120 the methodology sets a flag indicating that
the thermostat rationality test passed, clears a flag indicating
that the rationality test is in progress, and sets a test complete
flag. In 122 the methodology calculates the difference between the
pass threshold and the actual integrated error. The integrated
error comes from 86 while the pass threshold comes from the 2d
table lookup as a function of ambient air temperature. From 122,
the methodology continues to 104 and ends pending a subsequent
execution.
[0118] If the accumulated integrated error value is less than the
pass threshold value at 118, the methodology continues to 124. In
124 the methodology determines whether the integrated error value
at the time the diagnostic test was run is less than the value of
the highest integrated error required to fail the test. This fail
threshold is obtained from a 2d table lookup based on ambient air
temperature. If so, the thermostat is deemed to have possibly
failed the test and the methodology advances to 125. In 125 the
methodology determines if the aggressive counter is greater than
the aggressive counter threshold value. In not, the thermostat is
deemed to have failed the test and the methodology advances to 126.
In 126 the methodology sets a flag to show that the thermostat
rationality test failed, clears a flag indicating that the
rationality test is in progress, and sets a test complete flag. In
127 the methodology determines the difference between the fail
threshold and actual integrated error. The integrated error comes
from 86 while the fail threshold comes from the 2d table lookup
based on ambient air temperature. From 127, the methodology
continues to 104 and ends pending a subsequent execution.
[0119] If the aggressive counter in 125 is greater than the
aggressive counter threshold value, a no test condition is deemed
to exist and the methodology advances to 128. In 128 the
methodology sets an aggressive no test flag to show that the
diagnostic test was aborted due to a high engine speed, clears a
flag indicating that the rationality test is in progress, and sets
a test complete flag. From 128, the methodology continues to 104
and ends pending a subsequent execution.
[0120] If the accumulated integrated error is greater than or equal
to the fail threshold at 124, the methodology continues to 130. In
130 the methodology sets an inconclusive flag indicating that the
integrated error value was lower than the pass threshold and higher
than the fail threshold and therefore the thermostat cannot
accurately be deemed to have passed or failed the test. The
methodology also clears the rationality test in progress flag and
sets the test complete flag. From 130, the methodology continues to
104 and ends pending subsequent execution.
[0121] Referring now to FIG. 6, 98 is reached when the predicted
engine coolant temperature variable is less than the predicted
engine coolant temperature threshold at 94 in FIG. 4. In 98 the
methodology determines whether the engine coolant temperature is
greater than or equal to an alternate engine coolant temperature
pass threshold. This threshold is preferably set according to an
industry or governmental prescribed standard. For example, within
20 degrees Fahrenheit of the thermostat opening temperature. If
not, the methodology advances to 132 and ends pending a subsequent
execution.
[0122] However, if the engine coolant temperature is greater than
the pass temperature threshold at 98, the methodology continues to
134. In 134 the methodology sets a plurality of pre-selected
values. For example, the methodology sets the predicted engine
coolant temperature at the time the diagnostic test is run equal to
the predicted engine coolant temperature from 84; the engine
coolant temperature at the time the diagnostic is run equal to the
actual engine coolant temperature; the time since the diagnostic
test was run equal to the engine run time since startup; the
average vehicle speed at the time the diagnostic test is run equal
to the average vehicle speed from 90; the predicted engine coolant
temperature integrated error at the time the diagnostic test is run
equal to the accumulated integrated error determined at 86; the
ambient air temperature at the time the diagnostic test is run
equal to the ambient air temperature; and sets a flag to show that
the pass temperature threshold based rationality test ran.
[0123] In 136 the methodology determines whether the vehicle has
had a sufficient cold soak. This is preferably determined by
comparing the difference between the engine coolant temperature at
startup and the ambient air temperature with a temperature
difference threshold such as 5 to 15 degrees Fahrenheit. If so, no
test is run and the methodology advances to 138. In 138 the
methodology sets a flag to show that the diagnostic test was
aborted due to an insufficient soak, clears a flag indicating that
the rationality test is in progress and sets a test complete flag.
From 138, the methodology continues to 132 and ends pending
subsequent execution.
[0124] If the startup engine coolant temperature less the ambient
air temperature is less than or equal to the temperature threshold
to ensure a sufficient soak in 136, the methodology deems the
thermostat to have passed the test and continues to 140. In 140 the
methodology sets a flag to show that the thermostat rationality
test passed, clears a flag indicating that the rationality test is
in progress and sets a test complete flag. From 140, the
methodology continues to 132 and ends pending subsequent
execution.
[0125] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *